Treatment of cracked hydrocarbon distillates



Patented May 26, 1953 TREATMENT OF CRACKED HYDROCARBON DISTILLATES Charles Wankat, Brookfield, and Esbon Y. Titus,

Chicago, 111., assignors to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware No Drawing. Application October 10, 1951, Serial No. 250,782

4 Claims. (01. 196-41) This invention relates to the treatment of cracked hydrocarbon distillates and more particularly to an improvement in the process for treating cracked hydrocarbon distillates to effect both sweetening and reduction in the gum content thereof. 1

One method of treating sour cracked hydrocarhon distillates is to incorporate a chemical sweetening agent therein and to thereby obtain sweetening of the distillate within a short time in storage. However, it has been found that, while this method will effect the desired sweetening, in many cases it results in an excessive increase in the gum content of the gasoline. One method of treating the gasoline to reduce gum formation is to treat the gasoline, after addition of the chemical sweetening reagent, with caustic solution. However, it has now been found that the caustic solution used in this process becomes deactivated after several days use and no longer serves the efiective purpose of reducing gum formation in the gasoline. The present invention is directed to a novel method of treating the caustic solution in order to improve its active life and thereby to permit reusing thereof, with the con- I comitant savings in cost and alleviation of the disposal problem.

While the novel features of the present invention are particularly applicable for use in a process for the treatment of cracked gasoline containing mercaptans, it is understood that the novel features may be utilized in the treatment of mixtures of cracked gasoline and straight run gasoline, as well as hydrocarbon 'distillates heavier than gasoline including kerosene, gas oil, burner oil, diesel fuel, lubricating oil, fuel oil, etc. The sour hydrocarbon distillate preferably is first treated with an alkali metal hydroxide in order to remove a substantial proportion of the mercaptans contained therein. While caustic solution is generally preferred because of its ready availability and low cost, it is understood that other suitable alkali metal hydroxides may be used including potassium hydroxide, lithium hydroxide, rubidium hydroxide and caesium hydroxide, although not necessarily with equivalent results. In some cases an alkaline earth metal hydroxide may be employed including calcium, strontium and barium hydroxide.

The hydrocarbon distillate treated in the above manner is then sweetened by means of a suitable chemical sweetening agent. Aparticularly preferred chemical sweetening agent comprises a phenylene diamine type inhibitor and more par-' ticularly N,N' di secondary-butyl-p-pheny1ene diamine. However, it is understood that other phenylene diamine inhibitors may be employed including N,N-di-alkyl-p-phenylene diamines in which the alkylgroups contain from 1 to about 12 carbon atoms per molecule including such compounds as N,N'-di-iso-propyl-p-phenylene diamine, N,N-di-amyl-p-phenylene diamine, N,N- di-hexyl-p-phenylene diamine, etc., as well as those in which the alkyl groups are different as, for example, in such compounds as N-propyl-N' butyl-p-phenylene diamine, N-butyl-N'-amyl-pphenylene diamine, N-hexyl-N'-octyl-p-phenyl ene diamine, etc. While the phenylene diamine inhibitors generally are preferred, it is understood that other chemical sweetening agents may be employed including beta-naphthol, which preferably is used in admixture with an alcohol ineluding methyl alcohol, ethyl alcohol, etc., an alkanol amine including ethanol amine, propanol amine, butanol amine, etc., an amide including acetamide, propyl amide, butyl amide, aromatic amides, etc. However, it is understood that these chemical sweetening agents are not necessarily equivalent but all of them will be efiective in most cases to effect reduction in mercaptan content.

Because the sweetening reaction includes the conversion of mercaptans to disulfides, presumably through an oxidation reaction, it is essential that air or other oxidizing agent be present in the reaction. Generally suflicient air will be dissolved or entrained in the hydrocarbon distillate in order to satisfy this requirement. However, where sufficient air is not so dissolved, air from an extraneous source may be added to the hydrocarbon distillate. other oxygen-containing gases may be used in place of air. In some cases other oxidizing agents such as peroxides, permanganates, etc. may be employed.

In some cases it is desirable to efiect the sweetening reaction in the presence of an alkaline reagent. Generally the alkaline reagent will be used in small amounts which usually will not exceed about 5% by volume of said distillate. For convenience in subsequent separation, the alkaline reagent preferably comprises an aqueous solution thereof and still more preferably an aqueous solution of the alkaline reagent used in the treating step hereinbefore set forth. Thus, when the original alkaline treating step is effected in the presence of an aqueous caustic solution, an aqueous caustic solution is conveniently utilized during the sweetening reaction.

As hereinbefore set forth, the hydrocarbon dis- It is understood that oxygen or v tillate sweetened in the above manner in many cases will result in an excessive formation of gum in subsequent storage. One method of reducing this gum formation is to further treat the gasoline with an alkaline reagent. In general it is preferred that the alkaline reagent be of comparatively high concentration, caustic solutions of above about 25 Baum gravity being satisfactory. However, it is understood that the other alkaline reagents as hereinbefore set forth may be employed but not necessarily with equivalent results. One difiiculty which has been encountered through the use of this final caustic treatment is that the caustic can be used satisfactorily for only several days and then loses its capacity to effectively reduce gum formation in the hydrocarbon distillate. As hereinbefcre set forth, the present invention is directed to a novel method of treating the caustic used in this treatment in order to increase the useful life thereof. This improvement results not only in an important economical savings to the refiner but also reduces the quantity of caustic which must be disposed of.

In one embodiment the present invention re lates to an improvement in the process wherein a sour hydrocarbon distillate is sweetened by incorporating therein a chemical sweetening agent, then treated with an alkaline reagent to reduce gum formation, and the used alkaline reagent is separated from the treated distillate. which comprises separating the alkaline reagent into two layers, separately withdrawing each of said layers, and reusing the lower layer thereof to treat a hydrocarbon distillate as aforesaid.

In a specific embodiment the present invention relates to an improvement in the process wherein cracked gasoline is sweented by incorporating therein a phenylene diamine inhibitor, then treated with caustic solution of at least about 25 and preferably at least about 40 Baum gravity to reduce gum formation, and the used caustic solution is thereafter separated from the treated gasoline, which comprises separating the caustic solution into two layers, separately withdrawing each of said layers, discarding the upper layer, and reusing the lower layer to treat further quantities of said gasoline.

As hereinbefore set forth, the present inventors have discovered that the caustic solution used in the final treatment to reduce gum formation will separate into two layers and, in accordance with the present invention, each of the layers is separately Withdrawn. The upper layer is discarded from the process and disposed of in any suitable manner. The lower layer is recycled within the process for further use to treat additional quantities of the hydrocarbon distillate in order to reduce gum formation in storage. Not only does this improved process permit further use of the caustic solution in the process, thereby representing a considerable savings in cost. but also considerably reduces the amount of caustic solution to be disposed of. Because of the alkaline character of the spent caustic solution, disposal thereof creates quite a problem in order to avoid contamination of water streams, etc.

The final caustic treatment of the sweetened gasoline may be effected in any suitable manner, including a batch or continuous type of operation. Regardless of the method employed, the caustic solution, after it has lost its effective properties in reducing gum formation in the gasoline, isallowed to settle into two layers.

settling may be effected in any suitable manner and generally will comprise introducing the spent caustic solution into a settling tank and allowing it to remain therein until the caustic solution separates into two layers. The upper layer may be removed therefrom in any suitable manner and disposed of as desired. The lower layer is separately removed from the settling zone and is recycled to the final treating step of the process in order to treat additional quantities of the sweetened hydrocarbon distillate.

After treatment in the above manner, the gasoline may be water washed and/or filtered desired. This treatment may be effected in any suitable manner.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same.

The gum content of the gasoline reported in the following examples was determined by the Copper Dish Method which is a standard method of determining gum in gasoline. According to this method, ml. of gasoline is placed in. a copper dish and the gasoline is evaporated in approximately 3 hours by means of a steam bath. The weight of residue in the copper dish is reported as mg. of copper dish gum per 100 ml. of gasoline.

Example I The gasoline used in this example is a Mid- Continent thermally cracked gasoline havingan end boiling point of 360 F. and a mercaptan sulfur content of 0.0167% by weight. A sample of this gasoline is caustic treated and inhibited with 0.01% by weight of N,N'-disecondar,-"-. butyl-p-phenylene diamine. The gasoline is sweet after 48 hours in storage but will have a copper dish gum content of 139 mg. When the gasoline, after sweetening in the above manner, is treatedwith 47 Baum gravity caustic. water washed and filtered, the copper dish gum content will be reduced to below about 15 mg.

However, the 47 Baum gravity caustic solu tion used to treat the sweetened gasoline will lose its effectiveness in reducing gum formation after use for about 4 days. In accordance with the present invention, the used caustic solution is separated into two layers, the upper layer separately withdrawn and disposed of, and the lower layer is recycled for further use in the process. Further use of the caustic in this manner will serve to reduce the copper dish gum of the sweetened gasoline.

Example II The gasoline used in this example was a Pennsylvania thermally cracked gasoline which, after conventional caustic treating, had a mercaptan sulfur content of 0.022% by weight. 0.006% by weight of N,N'-di-secondary-butyl-p-phenylene diamine was added and the gasoline became sweet in 8 days in storage. This gasoline, after water washing and filtering, had a copper dish gum of mg. When treated with fresh 48 Baum gravity caustic, the inhibited gasoline had a copper dish gum of 63 mg.

In accordance with the present invention, the caustic solution was allowed to settle into two layers and each was separately recovered and used as follows: When another sample of the gasoline was treated with the upper layer, the gasoline had a copper dish gum of 1-19 me. When another sample of the gasoline was treated with a mixture of the upper and lower layers, it had a copper dish gum of 103 mg. When another" sample of the gasoline was treated with a mixture of fresh 48 Baum gravity caustic and the upper layer, the gasoline had a copper dish gum of 110 mg.

When another sample of the gasoline was treated with the lower layer, it had a copper dish gum of 60 mg. which, it will be noted, is of the order of that obtained through the use of the fresh caustic and is approximately one half of the copper dish gum content of the gasoline sample treated with the upper layer, as well as being considerably lower than that obtained by treating the gasoline with a mixture of the upper and lower layers or of a mixture of the upper layer and fresh 48 Baum gravity caustic.

The data reported in this example were obtained in a gasoline having an unusually high mercaptan sulfur content prior to inhibitor sweetening. This high mercaptan sulfur content sample was used in order to clearly demonstrate the advantages of the present invention. When using a gasoline charge having a lower mercaptan content, the copper dish gums of the final product will be lower. However, it is usual practice to blend thermally cracked gasoline with straight run gasoline, and the blended gasoline will have a considerably lower copper dish gum content.

We claim as our invention:

1. In a process wherein a sour hydrocarbon distillate is sweetened by incorporating therein a phenylene diamine inhibitor, then treated with an alkali metal hydroxide solution to reduce gum formation and the used solution is thereafter separated from the treated distillate, the improvement which comprises separating the used solution into two layers, separately withdrawing each of said layers, and reusing the lower layer thereof to treat a hydrocarbon distillate as aforesaid.

2. In a process wherein a cracked hydrocarbon distillate is sweetened by incorporating therein a phenylene diamine inhibitor, then treated with an alkali metal hydroxide solution to reduce gum formation and the used solution is thereafter separated from the treated distillate, the improvement which comprises separating the used solution into two layers, separately withdrawing each of said layers, and reusing the lower layer thereof to treat a hydrocarbon distillate as aforesaid.

3. In a process wherein sour cracked gasoline is sweetened by incorporating therein a phenylene diamine inhibitor, then treated with an alkali metal hydroxide solution of at least about 40 Baum gravity to reduce gum formation and the used solution is thereafter separated from the treated gasoline, the improvement which comprises settling the used solution into two layers, separately withdrawing each of said layers, discarding the upper layer, and reusing the lower layer to treat additional quantities of the cracked gasoline.

4. In a process wherein sour cracked gasoline is sweetened by incorporating therein a phenylene diamine inhibitor, then treated with potassium hydroxide solution of at least about 40 Baum gravity to reduce gum formation and the used potassium hydroxide solution is thereafter separated from the treated gasoline, the improvement which comprises settling the used potassium hydroxide solution into two layers, separately withdrawing each of said layers, discarding the upper layer, and reusing the lower layer to treat additional quantities of the cracked gasoline.

CHARLES WANKAT. ESBON Y. TITUS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,581,117 Love Jan. 1, 1952 2,589,450 Stanton Mar. 18, 1952 OTHER REFERENCES Rosenwold, Petroleum Processing, 6 969-973 (1951). 

1. IN A PROCESS WHEREIN A SOUR HYDROCARBON DISTILLATE IS SWEETENED BY INCORPORATING THEREIN A PHENYLENE DIAMINE INHIBITOR, THEN TREATED WITH AN ALKALI METAL HYDROXIDE SOLUTION TO REDUCE GUM FORMATION AND THE USED SOLUTION IS THEREAFTER SEPARATED FROM THE TREATED DISTILLATE, THE IMPROVEMENT WHICH COMPRISES SEPARATING THE USED SOLUTION INTO TWO LAYERS, SEPARATELY WITHDRAWING EACH OF SAID LAYERS, AND REUSING THE LOWER LAYER THEREOF TO TREAT A HYDROCARBON DISTILLATE AS AFORESAID. 